JPH0532889B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor layer and a surface oxidation layer (dielectric layer).
The present invention relates to a method of manufacturing a surface reoxidation type semiconductor ceramic capacitor having the following methods.

[Prior Art] When manufacturing a surface reoxidation type semiconductor ceramic capacitor, a surface reoxidation layer (dielectric layer) is formed on the entire surface of the semiconductor layer. Therefore, if a pair of capacitor electrodes made of a noble metal (non-reducible material) is provided with the surface reoxidation layer left as is, one surface reoxidation layer (dielectric layer) and semiconductor layer (dielectric contributing layer)
and the other surface reoxidation layer (dielectric layer) are interposed.
As a result, the effective dielectric layer thickness becomes the sum of the two surface reoxidation layers, resulting in a decrease in capacitance.

A method to solve this kind of drawback is to physically polish a part of the surface reoxidation layer to expose the semiconductor layer and connect one electrode thereto, and to connect base metals (reducible A method is known in which a metal) paste is applied to a portion of the surface reoxidized layer and baked to reduce the surface reoxidized layer and make it conductive, thereby forming an electrical connection to the semiconductor layer. According to these methods, only one surface reoxidation layer (dielectric layer) is interposed between a pair of electrodes, so the effective dielectric thickness is halved and the capacitance is approximately doubled. become.

[Problems to be Solved by the Invention] By the way, when surface reoxidation type semiconductor ceramic capacitors are mass-produced using these methods, the following problems arise.

(1) In the case of the former method of removing the re-oxidized layer by physical polishing, microracks are generated due to the mechanical force applied to the porcelain element, resulting in a deterioration in the characteristics and reliability of the capacitor. Although it is possible to suppress the mechanical force during polishing to prevent microcracks, the production efficiency will be significantly reduced.

(2) In the latter method using base metal paste,
In the method of using base metal paste, if the base metal paste comes into contact with other porcelain bodies, that part will be reduced and the insulation properties will be significantly reduced, so it is necessary to prevent the porcelain bodies from coming into contact with each other. Paste baking efficiency deteriorates. Also,
Base metal powder floats in the firing furnace and adheres to the re-oxidized layer on the surface of the porcelain body, causing insulation deterioration.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing a surface reoxidation type semiconductor ceramic capacitor, which can improve mass productivity and reduce characteristic deterioration.

[Means for Solving the Problems] To achieve the above object, the present invention includes a step of preparing a cylindrical ceramic body consisting of a cylindrical semiconductor layer and a surface oxidation layer of the semiconductor layer; arranging carbon powder or a substance containing carbon powder so as to contact at least a portion of the surface oxidation layer in the hollow part of the element body; heating the carbon powder or substance containing carbon powder and the cylindrical porcelain element body; reducing the surface oxidized layer with the carbon powder; and forming a first electrode layer made of a non-reducible material on the surface oxidized layer on at least a portion of the outer peripheral surface of the cylindrical ceramic body. and forming a second electrode layer made of a non-reducible material so as to be connected to the semiconductor layer through the reduced region of the hollow part of the cylindrical ceramic body. The present invention relates to a method of manufacturing a type semiconductor ceramic capacitor.

[Function] In the present invention, the hollow portion of the cylindrical porcelain body has the function of trapping carbon powder or its inclusions (for example, paste) therein. Therefore, even if the outer circumferential surfaces of a plurality of ceramic bodies come into contact with each other during mass production, there will be no reduction in insulation due to reduction of the oxide layer. Furthermore, compared to the property deterioration that occurs when a base metal is used as a reducing substance due to the base metal drifting in the furnace and adhering to the oxide layer, the above-mentioned property deterioration occurs when carbon is used as a reducing substance. few.

[First Example] Next, a method for manufacturing a surface reoxidation type ceramic capacitor according to a first example of the present invention will be described with reference to FIGS. 1A to 1C.

First, we weighed 94.5 mol% of high purity (99.5% or higher) barium titanate (BaTiO ₃ ), 5 mol% of neodymium oxide (Nd ₂ O ₃ ), and 0.5 mol% of manganese oxide (MnO) as a mineralizing agent. Then, wet mixing was performed using a resin pot containing an alumina ball.
Next, after dehydrating and drying this mixture, 8% by weight of a cellulose type binder, 10% by weight of glycerin, and water were added thereto, thoroughly kneaded, and extruded into a cylindrical shape.

Next, this molded body is placed in an atmospheric (oxidizing) atmosphere.
A sintered body was obtained by firing at 1300℃ for 2 hours, and after cooling it once to room temperature, N ₂ 90% +
Heat treated at 1000℃ for 2 hours in a reducing atmosphere of 10% _H2 , then heated at 900℃ in the air (oxidizing atmosphere).
Heat treatment (reoxidation treatment) was performed for 2 hours. This results in
As shown in FIG. 1A, a cylindrical ceramic body 3 consisting of a semiconductor layer 1 and a surface reoxidation layer (dielectric layer) 2 is obtained.

Next, as shown in FIG. 1B, a paste layer 5 containing 10% carbon made of carbon powder and an organic binder is applied on the surface reoxidation layer 2 of the hollow part 4 of the porcelain body 3 by a coating method. Formed.

Next, the carbon powder-containing paste is thermally decomposed by placing a large number of porcelain bodies 3 into a heating furnace so that their outer peripheral surfaces are in contact with each other and heat-treating them at 800°C for 2 hours in the atmosphere. The oxygen in the surface reoxidized layer 2 was removed by carbon, and that portion was reduced. That is, by reducing a portion of the surface reoxidized layer 2, that portion was returned to a semiconductor layer. Note that the adhesion force of the carbon powder to the ceramic body 3 after the reoxidation treatment is extremely weak, so that it is easily removed.

Next, silver (Ag) paste, which is a noble metal (non-reducible) electrode material, is applied and baked at 800°C for 15 minutes to form the first and second electrode layers 6, shown in FIG. 7 was formed. This silver paste baking treatment was carried out with the porcelain bodies placed in a furnace so that their outer peripheral surfaces were in contact with each other. first electrode 6
is formed on the surface reoxidation layer 2 on the outer peripheral surface, and the second
The electrode 7 is formed so as to be in contact with the semiconductor layer 1 in the hollow portion, and is also formed so as to extend over a part of the outer peripheral surface through the end face.

The electrical characteristics of 200 samples (capacitors) obtained were measured and the average values were found; the capacitance was 675nF/cm ² , tanδ was 2.8%, insulation resistance was 10 ¹⁰ Ω or more, and DC breakdown voltage was 1.0. It was warm at kV.

For comparison, a ceramic capacitor was formed using the same method as in this example, except that the reduction process using the carbon-containing paste was not performed, and the electrical characteristics were measured using the same method. The capacitance was 350 nF/cm ² , tanδ was 2.1%, insulation resistance was 10 ¹⁰ Ω or more, and DC breakdown voltage was 1.2 kV.

As is clear from the comparison of the capacities of this comparative example and this example, it is clear that a reducing action by carbon occurs in this example.

For comparison, a paste layer of Zn, which is a base metal, was provided in place of the carbon-containing paste layer 5 in FIG.
A ceramic capacitor was made by baking an Ag paste layer on the outer surface, and its electrical characteristics were measured. The capacitance was 680nF/cm ² , tanδ was 3.5%, insulation resistance was 10 ⁷ Ω or more, and DC breakdown. The voltage was 0.13kV.

As is clear from the comparison of insulation resistance and breakdown voltage between this comparative example and this example, the decrease in insulation resistance and breakdown voltage is extremely small by using carbon.

In order to investigate changes in characteristics due to changes in the carbon content of the carbon-containing paste, a ceramic capacitor was made with the carbon content of the carbon-containing paste set to 50% and the other conditions were the same as in the above example, and the characteristics were investigated. However, the capacitance was 680nF/cm ² , tanδ was 2.2%, insulation resistance was more than 10 ¹⁰ Ω, and DC breakdown voltage was 0.9 kV.

[Second Example] A ceramic body 3 consisting of a semiconductor layer 1 and a reoxidation layer 2 shown in FIG. 2 is formed by the same method as in the first example, and the hollow part 4 is filled with carbon powder 5a. This was then heat treated at 800℃ for 2 hours in the air, and then
The first electrode is made of Ag baked electrode as in the first embodiment.
When a second electrode was formed and its electrical characteristics were measured, the capacitance was 683 nF/cm ² , tan δ was 2.0%, insulation resistance was 10 ¹⁰ Ω or more, and DC breakdown voltage was 0.9 kV.

[Modifications] The present invention is not limited to the above-described embodiments, and, for example, the following modifications are possible.

(1) The carbon-containing paste layer 5 may not be provided on the entire wall surface of the hollow portion 4, but may be provided only on a portion thereof.

(2) The second electrode layer 7 may be provided in the entire area of the hollow portion 4. Further, it is also possible to adopt a configuration in which the second electrode layer 7 is not led out to the outer circumferential surface. Moreover, the first electrode layer 6 can be extended on the end surface of the ceramic body 3.

(3) Electrodes can be formed from noble metals (non-reducible metals) other than silver.

[Effects of the Invention] As is clear from the above, the present invention has the following effects.

(b) A hollow part is provided in the porcelain element, and carbon or a substance containing carbon is brought into contact with the oxidized layer in this hollow part to reduce the oxidized layer. Even if they come into contact with each other, the insulation of the oxide layer on the outer peripheral surface does not deteriorate.
Therefore, mass production of surface reoxidation type ceramic capacitors with good characteristics becomes possible.

(b) Since the reducing substance is carbon rather than a base metal, there is little deterioration in insulation due to attachment of the reducing substance to areas other than desired areas.

[Brief explanation of the drawing]

FIGS. 1A, B, and C are cross-sectional views showing the surface reoxidation type ceramic capacitor according to the first embodiment of the present invention in order of process, and FIG. 2 is a surface reoxidation type ceramic capacitor according to the second embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1...Semiconductor layer, 2...Oxide layer, 3...Porcelain element, 4
... hollow part, 5 ... carbon-containing paste layer, 6 ... first electrode layer, 7 ... second electrode layer.

Claims (1)

[Scope of Claims] 1. A step of preparing a cylindrical ceramic element comprising a cylindrical semiconductor layer and a surface oxidation layer of the semiconductor layer, and at least a portion of the surface oxidation layer in the hollow part of the cylindrical ceramic element. heating the carbon powder or carbon powder-containing material and the cylindrical porcelain body to reduce the surface oxidation layer with the carbon powder; A first electrode layer made of a non-reducing material is formed on the surface oxidation layer on at least a portion of the outer peripheral surface of the cylindrical porcelain body, and forming a second electrode layer made of a non-reducible material so as to be connected to the semiconductor layer through the reduced region.